v0.2.1-beta.4

Override packages and a real asset browser

Overrides become self-contained packages that can overlap without refusing each
other, and the asset browser gains sound auditioning, pinning, folder trees and
29 new textures.

New

• Add declarations DOOM never shipped, through override packages.
• Pin a shortlist of assets, and browse sounds by soundbank as a folder tree.

Improved

• Overlapping override packages compose instead of refusing each other.
• Prefab previews are interactive, and the Studio workspace is unified.

Fixed

• Every material is searchable, and a timeline larger than 1 MB opens.

Plus 57 smaller fixes and internal changes.